Abstract: PURPOSE: To study if the pharmacokinetic parameters derived from dynamic contrast-enhanced magnetic resonance (DCE-MR) images of the patellar cartilage are influenced by the main magnetic field strength. MATERIALS AND METHODS: DCE-MR images of the knee were obtained from 16 normal male subjects (eight cases in each 1.5 and 3T magnets). Also, four volunteers were evaluated in both equipments within 1 week. Cartilage pharmacokinetic parameters of vascular permeability (K(trans)), extraction ratio (k(ep)), extravascular extracellular space volume fraction (v(e)) and intravascular space volume fraction (v(p)) were obtained. RESULTS: Statistically significant differences were observed between the 1.5 and 3T groups for K(trans) (mean+/-S.D.; 5.44+/-2.27 vs. 1.01+/-0.41, respectively) and v(e) (3.37+/-2.32 vs. 0.81+/-0.80). A difference in K(trans) was also present when the same controls were evaluated in both equipments. There were no significant differences for k(ep) and v(p) values. Reproducibility of the pharmacokinetic calculations, assessed with the 24 acquisitions, showed a very low test-retest root mean square coefficient of variation (0.13, 0.10, 0.23 and 0.18 for K(trans), k(ep), v(e) and v(p), respectively). CONCLUSION: Cartilage vascular permeability values are influenced by the MR field strength. This should be taken in consideration when analyzing this biomarker.

Abstract: OBJECTIVE: The purpose of this study was to investigate the in vivo morphologic and elastic parameters of trabecular bone with high-resolution 3-T MRI in a healthy reference population. SUBJECTS AND METHODS: A series of wrist MR images were acquired with high-spatial-resolution (180 mum) isotropic voxels from 40 subjects without reported bone disease. After image postprocessing, the bone volume-to-total volume ratio, trabecular thickness, trabecular separation, and trabecular number were calculated in the morphologic analysis. Trabecular bone was mechanically simulated using the finite-element method to calculate the apparent elastic modulus parameter. The relationship between morphologic and mechanical parameters was studied. The influence of the analyzed bone volume was also investigated. RESULTS: Statistically significant sex influences were found on the bone volume-to-total volume ratio (p = 0.003), trabecular thickness (p = 0.02), and apparent elastic modulus (p = 0.01); these parameters were lower in women. However, trends were found only on trabecular separation (p = 0.06) and trabecular number (p = 0.07). Age had no statistically significant influence in any morphologic (bone volume-to-total volume ratio, r = -0.24, p = 0.13; trabecular thickness, r = -0.03, p = 0.88; trabecular separation, r = 0.12, p = 0.47; and trabecular number, r = -0.23, p = 0.16) or elastic (apparent elastic modulus, r = -0.18, p = 0.26) parameter. A statistically significant relationship between apparent elastic modulus and the square of bone volume-to-total volume ratio was found (r = 0.968, p < 0.001). This association was not seen (r = 0.185, p = 0.25) and apparent elastic modulus results were considerably different (p < 0.001) if the volume of analyzed bone was reduced. CONCLUSION: We found that bone volume-to-total volume ratio, trabecular thickness, and apparent elastic modulus are parameters significantly influenced by sex. Apparent elastic modulus results show a relationship with bone volume-to-total volume ratio. Trabecular bone volume should be maximized for an appropriate mechanical analysis.

Abstract: As Bone Mineral Density has been demonstrated to be insufficient to elaborate a correct diagnosis of bone diseases such as osteoporosis, a new software tool called EsTra has been developed in order to estimate the most significant structural parameters of trabecular bone microarchitecture. In EsTra, different techniques as automated segmentation, snakes, filtering, skeletonization, voxel classification and three-dimensional reconstruction are applied to Magnetic Resonance images of distal radius and ulna. A microarchitectural study is also carried out from three different viewpoints involving morphological, topological and fractal analysis. Results can be exported to a database to help the research of the disease and a clinical report is elaborated containing the most significant parameters obtained from the analysis.

Abstract: In order to help the assessment of trabecular bone diseases and complement Dual X-Ray Absorptiometry (DXA) in diagnosis process, it is needed an accurate mechanical characterization of trabecular bone structure to estimate the risk of fracture and evaluate micro-architecture deterioration. As Finite Element modeling has become a well-established method for analysis of complex structures, an algorithm has been developed to build a Finite Element mesh from three-dimensional reconstruction information in voxels. Generated mesh is loaded in a Finite Element analysis software in order to simulate micro-architecture mechanical behavior under compression conditions. Most part of related researches have been based on ex vivo micro-Computed Tomography (microCT) scans. This study uses three-dimensional trabecular bone reconstructions from high resolution Magnetic Resonance images acquired in vivo.